This invention relates generally to one-way clutches and more particularly to one-way roller clutches that have energizing springs that bias the rollers toward an engaged position where the rollers are wedged between the races so that one race drives the other in one direction.
One-way roller clutches typically have a plurality of energizing springs, generally accordion shaped, that are attached to a cage that is anchored to a cam race. Each spring individually engages and biases one of several rollers toward an engaged position wedged between one of several cam surfaces of the cam race and a cylindrical surface of an associated cylindrical race. See for instance U.S. Pat. No. 3,904,005 granted to Horst Husmann for an Overrunning Clutch Sep. 9, 1975; U.S. Pat. No. 3,955,659 granted to Fritz Ehret and Otto Worner for a Clamping Roller Freewheeling Device May 11, 1976; U.S. Pat. No. 3,994,377 granted to J. Russell Elsmore for an Overruning Clutch Retainer and Roller Assembly Nov. 30, 1976; U.S. Pat. No. 4,088,211 granted to John S. Dollar and Oscar G. Kitchen for a Overrunning Roller Clutch May 9, 1978; and U.S. Pat. No. 4,901,832 granted to Andre G. Werner for a Freewheel Drive Feb. 20, 1990.
The purpose of the energizing springs in applying a spring force to the rollers is to locate the rollers close to an engaged position when the one-way roller clutch is overrunning so that the rollers engage to lock-up the clutch almost immediately upon torque reversal. However, the energizing springs of the typical one-way roller clutches discussed above act independent of each other and consequently there is no guarantee that all rollers will engage at the same time and with the same force. Because of this, one or more rollers may not engage properly and "pop out" or uneven loading among the roller may occur leading to possible raceway brinelling by the highly loaded roller or rollers. It is also difficult to maintain raceway concentricity because some rollers may be wedged further into their cam areas than other rollers. Also failure of just one spring may result in complete clutch failure since one roller is not taking any share of the load.
In another less common, type of one-way roller clutch, the cage is not anchored to the cam race. Instead it is rotated with respect to the cam race to force all the rollers into or out of wedged engagement with the cam surfaces in unison. This "phasing cage" may be rotated by drag springs attached to the cage that ride on the associated cylindrical race or by an external actuator, such as a piston. See for instance, U.S. Pat. No. 5,101,946 granted to Frederick G. Lederman for a Cage Phased Roller Clutch Apr. 7, 1972.
A drawback of the passively actuated type roller clutch is that the drag springs tend to produce either high drag forces in the overrunning mode of operation that lead to excessive wear and high power consumption or light drag forces that lead to a long response time for clutch engagement and possibly no clutch engagement at all.
A drawback of the externally actuated type is that the actuation mechanism adds unnecessary bulk and increases space requirements. Moreover, as a practical matter, the one-way clutch is limited to applications where the cylindrical race free-wheels.